1. Field of the Invention
The invention relates to an alignment mark, a substrate, a set of patterning devices, and a method for manufacturing a device.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). When so used, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) of a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In practice, multiple patterns may be projected on top of each other to obtain a three dimensional product structure. It is important that multiple patterns are properly aligned with respect to each other. This overlay requirement is increasingly important with increasing resolution.
In lithography processes, double patterning methods such as Litho Etch, Litho Freeze, etc., may be used. Such techniques are used to enhance feature density on the substrate.
With the use of these techniques alignment of the first and second exposure on product resolution level has become even more important. Therefore, there is a need for a system and a method to determine alignment of a first and second exposure on both a macro level, as for instance used in conventional alignment measurement tools, and a micro level, for instance at product resolution level.
Several methods and measurement tools are available to measure overlay of multiple exposures. However, different methods and tools are suitable for different measurement ranges, and the measurement techniques of the different methods and tools cannot be (directly) compared.